1. Field of the Invention
The present invention relates to a femoral stem for an artificial hip joint used in the treatment of transcervical fracture in the hip joint, and an artificial hip joint that includes the same, particularly to a femoral stem having a greater trochanter plate disposed at the top of the femoral stem and an artificial hip joint that includes the same.
2. Description of the Related Art
A femur of an elderly person is often weakened due to progressed osteoporosis. As a result, when the femur of the elderly person is subjected to an external force that is not normally experienced due to falling down or other incidents, the femur may be broken in the neck of the proximal part of the femur. Such a fracture is referred to as transcervical fracture. The transcervical fracture is classified into an intracapsular fracture and an extracapsular fracture by the position where the fracture occurs, whether it is inside or outside of the joint capsule. The intracapsular fracture and the extracapsular fracture require different methods of treatment.
The extracapsular fracture is treated with a surgical operation that secures the head of femur and the femur by means of an internal fixation tool (CHS, nail, etc.) in anticipation of the coaptation of the bone. In case severing of the greater trochanter is involved, a treatment of securing the greater trochanter onto the femur is also carried out by using a greater trochanter plate. The greater trochanter plate is disposed on the outer surface of the greater trochanter and is fastened while being pressed toward the femur by means of a wire or the like, so that the greater trochanter is secured onto the femur.
In the case of the intracapsular fracture, on the other hand, there is a possibility of a blood vessel that serves the head of femur to have been cut off and causing necrosis of the head of the femur, and therefore a surgery to replace the head of femur with an artificial femur head is carried out. The replacement surgery includes such a technique as the greater trochanter is once severed so as to remove the head of femur and replace it with a femoral stem having an artificial head of femur, and the greater trochanter that has been severed is secured at the original position (Chanley technique). The greater trochanter that has been severed is secured by using the greater trochanter plate, similarly to the case of the extracapsular fracture described above.
The conventional greater trochanter plates that have been used include such forms that are called the plate or bone grip as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-217992 and Japanese Unexamined Patent Publication (Kokai) No. 11-76280. These greater trochanter plates are both formed in a configuration that fits to the curved exterior surface of the greater trochanter and has a plurality of through holes through which a cable is passed. These greater trochanter plates are used such that the greater trochanter plate is disposed on the outside of the greater trochanter, a wire is passed through a through hole formed in the greater trochanter plate and through a hole, that has been formed in a lesser trochanter of the femur in advance, and is wound around the femur before being clamped. Thus the greater trochanter is secured onto the femur.
Another form of the greater trochanter plate is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-179605 that describes a holding member to be used together with a femoral stem that has an artificial head of femur. The holding member is fixed after inserting the femoral stem into the femur and securing it therein. The holding member has wires attached on both sides of the holding member. The holding member is disposed on the outer surface of the greater trochanter, and is secured by winding the wires on both sides around the femur. At this time, the wires cross the femoral stem and are guided in a predetermined direction by a notch formed in the femoral stem, so as to be wound around the femur and secured.
The conventional treatment for extracapsular fracture is based on osteosynthesis. To achieve assimilation of a bone suffering from extracapsular fracture, firm fixation is an important factor as in the case of osteosynthesis for the other part of the bone. The extracapsular fracture is divided into a stable type and an unstable type from the view point of the stability of reduction. In the stable type such as fracture in the horizontal plane, fixation can be achieved relatively satisfactorily, and therefore it is permissible to apply a load to the fractured bone at an early state in the case of some surgical techniques. However, post-surgery recovery may often be unsatisfactory in elderly patients who have weakened bones. In the unstable type such as comminuted fracture of proximal femur accompanied by the fracture of the greater trochanter and/or lesser trochanter, it is very difficult to fix and therefore the fractured part must be relieved of load over a long period of time in order to prevent the bone from again suffering dislocation under load. With such a background, it is difficult for the patient to leave the sickbed and start walking in the early stage of recovery after surgery for the treatment of transcervical fracture, and there is little hope of keeping dementia from progressing and improving the QOL (quality of life). Thus the present-day requirements in the medical field are not yet satisfied.
In the treatment of extracapsular fracture and intracapsular fracture that require the greater trochanter to be fixed, the greater trochanter plate is secured onto the femur with wire thereby holding the greater trochanter on the outside of the femur. Since the holding force is applied in the horizontal direction, it is difficult to offset the force of the gluteus medius musculus that adheres to the greater trochanter and pulls up the greater trochanter. As a result, when the gluteus medius musculus repetitively pulls up the greater trochanter, the greater trochanter plate cannot resist the force of the gluteus medius musculus pulling up the greater trochanter and eventually it becomes impossible to secure the greater trochanter at a predetermined position of the femur thus allowing the greater trochanter to be displaced upward. Furthermore, there has been a possibility of the wire breaking, thus making it necessary to perform additional surgery.
The greater trochanter plate disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-217992 and Japanese Unexamined Patent Publication (Kokai) No. 11-76280 are secured by forming a through hole for passing wire in the lesser trochanter of the femur. However, many of the patients who suffer from fracture in the head of the femur are elderly people with weak bones. Boring a hole in the femur of such an old patient often causes a secondary fracture.